Chemically Anchored Rebar Perovskites for Deterministic Layer‐by‐Layer Integration

The large‐area deterministic integration of distinct halide perovskites into designed heterostructures is essential for advanced optoelectronics, but remains challenging due to solvent incompatibility, lattice mismatch, interfacial instability, and mechanical fragility. Here, we report a scaffold‐guided, layer‐by‐layer integration strategy that overcomes these limitations through a synergistic mechanical‐reinforcement and chemical‐coordination paradigm. Using a porous electrospun polyacrylonitrile nanofiber network as an active, coordinating macromolecular scaffold, we fabricate freestanding, large‐area rebar perovskite films with high perovskite content (>99 wt%), thickness tunability across orders of magnitude (sub‐µm to mm), and exceptional mechanical robustness. Beyond its physical role as a support matrix for perovskite deposition, the nanofibrous scaffold functions as an active interface‐coordinating regulator, which passivates interfacial defects, suppresses non‐radiative recombination, and directs crystallization. This platform enables the deterministic layer‐by‐layer integration of various perovskites into sharp‐interfaced two‐dimensional (2D)/ three‐dimensional (3D) heterostructures and complex 3D architectures with programmable composition and geometry. As a functional demonstration, a 2D/3D (PEA) 2 PbI 4 /MAPbI 3 rebar perovskite heterostructure achieves high‐sensitivity x‐ray detection with ultralow dark‐current drift and a self‐powered detection limit surpassing medical standard.